78 Scientific Intelligence. 



II. Geology and Mineralogy. 



1. Gravity Anomalies and their Geological Interpretation*. — 

 This article is in part a condensation of a more detailed paper by 

 the same author entitled "Die mediterranen Kettengebirge in 

 ihrer Beziehung zum Gleichgewichtszustande der Erdrinde." 

 (Abh. Sachs. Akad. d. Wiss., Bd. 38, 2. Leipzig, 1020.) The 

 article opens with some general explanations of the formulas for 

 theoretical gravity and of the methods for reducing gravity 

 observations for topography. This opening section contains two 

 or three statements not strictly correct, but these concern mat- 

 ters not generally understood except by specialists in gravity 

 work or in the theory of the figure of the Earth, and do not 

 essentially affect the conclusions reached. 



The Bouguer anomaly is used throughout the article as a 

 measure of the compensation. A single Bouguer anomaly meas- 

 ures, of course, merely the net effect of the compensation and of 

 the distant topography and affords no clue to the mass of the 

 compensation nor to its situation. Thus no allowance is made 

 by this method for the effect of nearness to the continental shelf, 

 but for nearly all of Europe this effect is practically negligible. 

 The advantages of using Bouguer anomalies are the ease with 

 which they are computed and the fact that they imply no par- 

 ticular depth or distribution of compensation, and that, when 

 gravity stations are sufficiently dense, they lend themselves, 

 according to Prof. Kossmat, to geological interpretation better 

 than the anomalies computed by the isostatic method. 



The article summarizes the results of Prof. Kossmat 's examina- 

 tion of known gravity anomalies in Europe, Asia, Africa and 

 North America. For the last-named the war has evidently pre- 

 vented him from receiving the more recent publications on the 

 subject. He maintains that mountain chains are not caused by 

 a swelling of the crust in their vicinity but by the folding under 

 tangential pressure of certain weaker portions of the crust. 

 Such a chain is not compensated by itself but only in connection 

 with the neighboring piedmont regions. The additional matter 

 imposed upon a given area by the folding may be partly com- 

 pensated by the sinking of that area under the additional load. 

 This sinking the author conceives as partly elastic rather than 

 entirely flotational, the substratum being bent under the load. 

 The result is that the compensation is regional rather than local. 

 In regard to the evidence on this subject offered by the 124 sta- 

 tions in the United States, the number treated in U. S. Coast and 

 Geodetic Survey Special Publication No. 12, which evidently 



* Die Beziehungen zwischen Schweranomalien und Bau der Erdrinde, by 

 Franz Kossmat. Geologische Eundschau, vol. 12, pp. 165-189. 1921. 



